Traditionally, there were two separate types of physical storage, main storage (MS) and expanded storage (ES). This has existed in data processing systems of various types, from the PC level to large parallel systems. This physical separation existed primarily due to architectural and machine absolute addressing limitations (for example, an ESA/390 machine can only address a maximum of 2 Gigabytes of main storage). However, with the advent of LPAR and future architectures and machines which may permit more than 2 Gigabytes of main storage to be addressed, today's physical separation does not provide an optimum storage utilization or reconfiguration capability. That is, the physical expanded storage can only be used as expanded storage and if it is not fully used by the active programs (application programs or the operating system) the unused expanded storage remains idle.
This is inefficient. It would be desirable to change the storage system to make it more flexible for operations while it is powered and operating.